AN  INVESTIGATION  OF  THE  CONTROL  OF  SOUND 
IN  VENTILATING  PIPES 


BY 

WALTER  BOATMAN  WORSHAM 

A.B.  University  of  Illinois,  1912 


THESIS 

SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS 
FOR  THE  DEGREE  OF  MASTER  OF  ARTS  IN  PHYSICS 
IN  THE  GRADUATE  SCHOOL  OF  THE 
UNIVERSITY  OF  ILLINOIS,  1922 


URBANA,  ILLINOIS 


■ - -r’’ 


* * *{  R 

'lfl\l04HO  jonnoo  iHH  HO  WllTADITgH’fPH  KA  '; 
,»3fU'I  DHn/.JlT'/l3V  i2r^^ 


n/jiTrAOH  saTJA?/ 

U*  l •K'^tf.l  )t>  ^Hiyviinr /I.A 


T » 


!"!{*  % 


JS  V'  ; 


K 


■/  ■ .*'^1 


1 -V' JlflKW . -J 'jLi 

''^V(.,%,  ^v- 


'JP. 


. ■ V'**' , V‘ 

y.^ 

'■  ■ *■'  "'  ' *L 

. -'ij  v f ' :t 

/ >'' 

^ T » ) 

^ )C?l4^1l‘i 

j , 4Mi“  Hii  tiifaiiJ>^Utr4  JAJT«M  VM 

* I'tvfiii.  HI  aiTiA  4»‘f : 

- uu  vj  M‘»n.rh5‘-  3t\y'nAi.^y;'-iiut  w> 

jr^  ^|0Hr4^if  . ,I>1l% 

«■/  /'i.  _ 

^ V'#A.^CO 

' ■ 'f , 


\A)09 


-H. 


UNIVERSITY  OF  ILLINOIS 


THE  GRADUATE  SCHOOL 


Jmix 


-IQ2-IU 


I HEREBY  RECOMMEND  THAT  THE  THESIS  PREPARED  UNDER  MY 


SUPERVISION  BY rALTEB^B" /^T~' AY 


ENTITLED Ail—LDIES TTOATTO-'  QE  Th^  Crr’rPOT,  ..XY 


VT^YTTT.AT  I :Njn  PTPVE 


BE  ACCEPTED  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR 


THE  DEGREE  OF  YAPTFB  OY  ABTB  TAT  PFTYP,rnq 


T.r.u) 


In  Charge  of  Thesis 


Head  of  Department 


Recommendation  concurred  in* 


Committee 


on 


Final  Examination* 


•Required  for  doctor’s  degree  but  not  for  master's 


M-  ' ..  . • ' M 


A '.Tcr 


ajoi/irrjt'  'fife  YTii^HHvma  . 


n , ' !<! 


JOOHJ*;,  HOT 

■ tv  m 


4 f\ 


tTHVvJ  «A^nA*tclilH  f^i^:<fri  ^ih*i  ' /in 

' 1 „ . '■  ‘ 


fc  ••'<■'  ■ lift  It#  i‘jf//i  r j t'-^. I jni 


/'JllotW/lltr  : 


m 


luHjTi 


i?  . 

j_,,*  ( 


'•"i  ■ 


. « 


»'■  >#iiifili  n>’ 


y.' 


»;  >;K'i.iii(x  ^,p.  I' 


,1 


'♦  'Pfc  -n^-<  ^ - ' 1 

’ •nirvivf-  i -' ? 


<i" 


iw^sJs'  l»/J 


ff 


. M -.:><  "i'  ' “''  ■ 


m'ty*  <*■'■■". >r':l  iur»^ 


e * 


ip* 


■ ,*'  . -'4?' 


TABLE  OF  CONTENTS 


I PURPOSE  OF  INVESTIGATION 
II  ACTION  OF  SOUND  IN  VENTILATING  PIPES 
III  PREVIOUS  INVESTIGATIONS 
IV  EXPERIIv'IENTAL  INVESTIGATION 
1.  General  Method 

a.  Source  of  Sound 

b.  Receivers 

1.  The  Ear 

2.  Instruments 

c.  Devices  to  Stop  Sound 
V RESULTS  OF  INVESTIGATION 

1.  Experiments  in  the  Smith  Memorial  Music 

2.  Experiments  in  the  Physics  Building 
VI  DISCUSSION  OF  RESULTS  AND  RECOMMENDATIONS 


Building 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/investigationofcOOwors 


I.  PURPOSE  OF  INVESTIGATION 


The  purpose  of  tnis  investigation  is  to  study  the  action  of 
sound  in  ventilating  pipes  and  to  seek  devices  that  will  serve  for 
its  control. 

The  insulation  of  sound  in  buildings  is  complex.  Soundproof ing 
investigations  carried  on  thus  far  have  been  concerned  chiefly  with 
the  action  of  sound-proof  wallSj  doors,  and  similar  constructions; 
little  attention  having  been  paid  to  the  transmission  of  disturbing 
noises  through  the  ventilation  ducts,  li^fithout  some  efficient  con- 
trol of  tile  sound  through  these  pipes,  it  is  a w-aste  of  effort  to 
construct  sound-proof  walls,  install  patent  dcors  or  other  contriv- 
ances for  insulation. 

II  ACTION  OF  SOUNE  IN  VENTILATING  PIPES 

Sound  v;aves  consist  of  alternate  condensations  and  rarefactions 
in  the  air.  The  air  particles  move  back  and  forth  over  very  short 
distances  in  transmitting  the  waves;  toe  action  being  entirely  dif- 
ferent from  the  passage  of  Vvrater  or  air  through  a pipe. 

Sound  waves  are  transmitted  fromi  one  room  to  another  through 
heating  and  ventilating  pipes  very  much  as  sound  is  carried  through 
speaking  tubes.  Instead  of  spreading  out  in  spheres  as  they  do  in 
the  open  air,  the  sound  v;aves  are  confined  within  the  duct  by  re- 
flection at  the  sides  sc  that  they  travel  for-ward  with  a comparative- 
ly small  decrease  in  amplitude,  the  wave  front  remaining  the  same 
throughout.  The  velocity  of  propagation  is  independent  of  the  press- 
ure of  the  air;  it  increases  with  the  temperature  of  the  air,  and 
is  propagated  quicker  with  than  against  the  air  current,  the  speed 
in  the  first  case  being  the  sum  and  in  the  second  the  difference  cf 
that  of  sound  and  the  air  current.^ 

1.  Barton,  E.H.  ’’Text-Bock  on  Sound”,  S-ac.4?3. 


■■•vt;iV»'.  • " ' '‘  ^m 

. : .74^  *’ •••.,■■  v%'V  '‘^«'%'V  ^ 


‘ K -■  ?-^A'  ■ f -:» '/  jfeft 


:x  j. . m 


* j,#l" "‘ 


■ J. 

- 


' ,r  ~ T’^  ’ 

■^'  / ■•'  ■„ 


i\  J-  'i 


« ^ y > 

''  f '»  ^ V 

•’  ■ * :^h  ^ *7  , *'■  ■* ’0407^" 


i 


i^f:z  \V  . V . 


A’  M»  W,.*: 


, i.„  R^'- 


. ■'  7,.i 


, *.^  >•  

..  !.■;  .-..ij^i- , . tWltffci:'.l^-i.fe4OT8a» 

* , ’ .!•,  ' . ':'"  tfvSE;  , . < *.  f t' 


kit 


- • '’  •*•'■»•  f • »*M<v-rF  !►  , > ‘W  • > '^t  « *•  V4*  “*  ••  ■ '«!«»^ 

'■  ' * 'i-  ■•  ''“  ffT^SS"  •'  1 V'ff  ^*i**'^ 

» ' - "■•■i  • frA ' f -^, 4t7-3  ii,. 


Ill  PREVIOUS  IWVESTIGATIONS 


2 

Scund  proofing  has  engaged  the  attention  of  architects  and  scien- 
tists for  years  but  little  effort  has  been  made  to  devise  plans  for 
sound  control  in  ventilating  pipes. 

Hiram  Percy  Haxim,  of  Hartford,  Connecticut,  made  a study  of  the 

3 

problem  and  later  patented  what  he  ternsd  a "Building  Silencer". 

This  device  consists  of  a large  chamber  which  is  to  be  placed  on  the 
top  of  a building  and  is  designed  in  such  a manner  that  all  the  air 
entering  or  leaving  the  building  must  pass  through  it.  It  is  lined 
with  scrne  sound  deadening  substance  and  fitted  with  coils  and  baf- 
fles arranged  in  such  a manner  as  to  transform  the  energy?'  of  the 
sound  into  heat;  energy.  It  v/as  designed  to  eliminate  outside  noises 
rather  than  to  stop  the  transmission  of  sound  between  rooms. 

Professor  Wallace  Clement  Sabine,  of  Harvard  University,  studied 
the  effect  of  air  currents  and  of  temperature  in  connection  with  his 
investigations  cf  architectural  acoustics. 2 He  concludes  that  the 
problem  cf  properly  heating  and  ventilating  a room  is  a difficult 
one  from  an  acoustical  standpoint  and  merits  consideration.  He  ad- 
vises that  the  t en-'perature  cf  a room  should  be  kept  homogeneous  and 
thinks  that  this  condition  cf  homogeneity  is  best  secured  by  that 
system  of  ventilation  knO'/m  as  "distributed  floor  outlets". 

Dr.  Paul  E.  Sabins,  Geneva,  Illinois'^  described  briefly  the  sys- 
tem installed  in  tne  Riveroank  Labcratoriss  and  brought  out  several 
important  factors  regarding  sound  control  in  ventilating  systems. 

His  method  is  very  similar  to  that  devised  by  Maxim. 

Professor  Floyd  Rows  Watson,  cf  the  Physics  Department,  UniversiV 

2.  Patent  No. 1,289,856,  dated  December  51,  1918. 

3.  Sabine,  W. C.  "Architectural  Acoustics",  Eng.Rec.,  June  1910. 

4.  Proceed.  Ill,  State  Acad.Sci.,  April  1323. 


^ 5 ■='>.•’••  -.  ■••  ' ‘ r-'v  ■ 


’■j'\i 


^ 4 J ■-  ..  . 





e ’ 


iLJ  ■:-  ■■7-'i  ■ ■ ■^”  ■ 


*’>  \V  i'* 


■ >■•  ■■  , •;'  >'  . '■  J 


ff 

, “,4, 

^#1'.  J 


,v.  .,_ 


! r,>' 


• * ^ 


■ *'f.  ' u i . • '-  »■' 

’ * - .-‘‘v, 

4%c.>t  iTl.i  txM 

'fiTjijs  ■>_  ' 


Si 


> *♦.; 


ft  1 


' t 


^3  t-,.i:  ^1/ .* 

: "ikL  J' ^ . .M 


fT  i' 


I I''  ,7  > ''  V •-  ^ •;  --ii 


m 


I-  ' A , »*v» 


■*t  ■;• 


- ■ -‘ft  ./£ '■  L-i r‘^'l;u.r‘f  ■ 


lit- . 


*^jv^  <•■  > jfc  ♦ A 

4>  #v  4 •)»  «•% 


i<*  *t 


•;■■  — • - |^:v- 


:-  ‘ -::‘T 


■jCie 


’•  .*;^,4f^v-  -‘.Ai 


\ "■'»  _ - '^”  ' r - 

i . '-At  Vi:i*?»i.t.Vi\P>-5 


'^Si 


:.S.' 


'10 


,.A«. 


t,  " 


M 


H's 


:fm 


m 


Sjt'  ''‘^ 


3 


of  Illinois,  has  studied  this  problem  in  connection  v;ith  his  v/ork  on 
architectural  acoustics.^  Dr.  Itatscn  rscommends  that  any  necessary 
openings  for  pipes,  ventilators,  etc.,  be  placed  in  outside  or  cor- 
ridor walls  where  a leakage  of  sound  will  be  less  objectionable;  and 
that  ventilation  systems  should  be  arranged  sc  as  to  minimize  the 
possibility  of  the  transmission  of  sound  from  room  to  room. 

Other  investigations  which  have  been  carried  on  and  which  deal 
more  or  less  directly  upon  this  subject  are  as  follows: 

Naval  Constructor  Elliott  Snow,  U.S.N.,  in  his  bulletin^ 
on  ’’Voice  Pipes”  describes  tests  made  to  determine  the  efficiency  of 
voice  tubes  on  battleships.  His  chief  conclusions  are  that  there  is 
a loss  of  intensity  in  tubes  of  small  diameter  due  to  the  friction 
in  the  directional  length  of  the  tube;  the  yielding  of  tne  material 
from  which  the  tubes  are  mads,  and  leakage  of  air  through  the  walls 
of  the  tubes  or  through  the  joints;  (Tnese  conclusions  w^ere  suggest- 
ed by  Professor  F. C.  Sabine)  also,  that  sound  is  strengthened  by  the 
neighborhood  of  a sonorous  body,  and  that  pipes  should  be  made  of  a 
ncn-vibrant  material,  they  should  be  as  smcctn  as  possible  inside 
and  thick  enough  to  prevent  losses  from  "panting”. 

Helmholtz  and  Kirchoff  investigated  the  velocity  of  sound 
in  pipes,  the  former  taking  into  consideration  the  friction  alone, 
\vhile  the  latter  considered  also  the  exchange  of  heat  between  the 
pipe  walls  and  tne  contained  gas,  and  both  came  to  the  conclusion 
that  the  difference  between  the  velocity  cf  sound  of  frequency  N in 
free  air  and  in  a pipe  cf  diameter  r,  is  inversely  prpportional  to 

7 

r,  and  inversely  proportional  to  the  square  root  of  N. 

5.  Vfatscn,  F.R.  "Sound-Proof  Partitions”,  Bull.  137  Eng.  Expt,  Sta. 

6.  Snow,  Elliott,  "Voice  Pipes”,  U.S.N.  Inst.Proc.,  Vol.35,  No. 3. 

7.  Capstick,  J.F.  "Sound”,  Sec.SoS. 


Aj  JLi  i‘iV4j  t 


* ,v  * ^ 

* 


■ :-Vr 


i 


, • 1. 1 < 
L'v 


’w  . 

' ■ 5.  <-  /•■<  ■•  ■ >!  iH 

-i'.f  ■ ■.  :,  t'  . vtM 


w>'4^ 


.‘*iJ 


% 


‘h)  r‘^ 

f.-i-  vfit t*j/.T  j-  *r..'  .-, '‘^V'wJC- ■#.  -.; 


1 - 

• to-i  :< ' , 


■c‘v 


•t » 


.■ «'  .'  1 , 


'■  {' 


^ i «’ 


' ' - "/f  : ■ I 

’.;•  L*-* 


*.  '*  ,\ 


- ; ■ ' » Tu'*  IT  )^J.'  JIt  1-' t W.i  ' t ; iMtl 

• '■*  Afic  - »,i  <*-> ' ^ .* . ■ 

' ■ i*  ■ ■ '>  ‘'  ■ ' ! 

*■ '.i  ' .■  5 'J  4 vl  ^ivr  w,  \Tk,  'f'x.C^;' 

f?'.  ^ u;;”  !t'|^ 


'i  } 

I , -v 
fv' 


; V(  XV 

,y  , '*  v'  ■*  *»■' 


t,^r  v*>'* 

,:.’J 


v;..  i r i ■•  ■ ' (?  .'  t-xi  J ' ' 


S 1 

J 


1 f. 


f > 


jrfvr’i>(kf  •>,;  -f  •■'  r,  - 4-  ^ 


:i  ?; 


:Vs  *t‘a 


U ‘ 


■.V 


L ■ MMi  J? 


■ L^- 


4 


Re^'^ault  an  extensive  serif's  cf  cbservcti^us  of  tne  v T' 


Iccity 

of  sound  in  pipes 

and  foux'i 

d t..v-t  the  V el 'City 

ap^r^' acn.es  a 

limit 

as  the  souna  grows 

fainter. 

the  limit  oei:,.-,  Ic. 

■ er  for  narrow 

pipes 

than  for  wide  ones. 

The  lirrdting  velocity  was 

tus  sa-.e  for 

sources  of  sound,® 

Capstiok  brings  cut  tne  fact  tnat  tnere  v^culd  be  oo;.  c reflection 
if  a pulse  traveled  along  a tuo;^  vliich  aad  a sudden  c:ian:-‘, e of  diaxii- 
eter,  for  example,  if  a ccrirpression  starts  fro;.'  A (Fig.ll  and  tr?u/el 


A 


B 


C 


Fig.l 

to  tne  right,  it  meets  v;it:h  lessened  resistance  on  reachin:.  B,  -over- 
runs itself,  ana  part  of  its  ensr;^y  is  refl-.^cted  oaok  to  A in  a 
rare  face  ion.  If  the  compression  stc.rts  from  C and  ravels  to.ards 
tne  left,  it  ..'sets  a greater  resistance  cn  reacnioo  B,  and  part  of 
its  energy  is  reflected  back,  to  C in  a compressivui.  In  eacn  case 
part  of  the  energy  gees  on  and  part  is  reflected,  and  the  ameunt  re- 
flected depends  cn  tne  relative  cross  sections  of  the  two  pacts  of 
the  tube.  If  there  is  little  orange  of  section  tuore  is  little  re- 
flection. “ 

-ne  author  r;:ade  a study  of  the  action  of  sound  ’.vaves  in 
register  boxes  designed  to  connect  each  rcc.  x^ith  t.t<e  vent  pipes. 
These  register  boxes  are  mads  larger  than  the  pipes  to  7.hich  they 

3.  Barton,  S.H.  "Text-^Book  of  Sound",  Sec.  478. 

9,  Gapstick.  "Sound",  Sec. 98. 


.rtf 


VI 


■’’?  ,-i'4t 


■ '-r^'.  tp-  - : ’♦  • dl!  ' • !l/if Vif. 


- : ■ . ^ Uit  - ' ?. "'  \ -,f  ^V"' 


■r  ' ^ 


|lw.  *rr  4^3%', ■ {4jr  .. 

•'  Iv; 

'*  ' • • .^  ■ ? ^ ..  ’■■*  ' '♦3r-  vH 


\P 


:j<'c'' 


> 


M 


.'  'j ' / 


r,v'^ 


■•  ’ >«■ 


,M4 


I *'-kf 


'M‘ 


-■■■?'  id  S: 

*f  i4.  ' 


i 


i ..  r4T.,:-»  .r'U’^w_o;^r  ^ ^ 


s Ut  '}-t>fi 


V ■ ■< 


3 . ^ ’ ‘Ji  - <«WF'BK " * i^-4[ 


f.^“ 


fiiji'' 


'iv. 


f^m 


" » 


' V .••';•  ■•  " ,./'>V.'^.  ; -T  Ai^mL  ,/S  ■ S^i'ft^lsStH  .v;,^ ' '‘vjS^SiAWfli 

;■  fr'  • 4loy^^-V»y, 


if: 


M' 


EM'iiifi' 


are  connect  5I  so  ■-i.s  to  n a 3 tna  net  free  area  of  'cac  re- is  ter  or 
grill  eciual  to  tne  area  cf  ta-  life,  Tnis  will  require  a resist rr 
havinq  a 50^’  free  area  to  be  twice  tne  size  of  tne  uact  ae,  ior  ex- 
airplcj  an  8"  x lo"  duct  will  a^ave  a 16”  x 16”  register  as  snown  in 
Fig.  2.  This  enlargem  ent;  Oriavs  cut  tae  pcini  maos  by  Capstick  as 
described  above.  For  this  investigation  of  the  sound-waves ^ special 


apparatus  was  devised^  cor^s  istin;;,,  of  a tank  witi-i  a glass  bet  ton;  on 
wnioh  tne  outline  model  cf  t'cese  register  boxes  was  placed,  Fater 
was  then  poured  in  the  tank  and  ripple  waves  generated  by  a streau.  ci 
compressed  air  wnich  was  interrupted  by  passing  throu^.h  a circle  of 
holes  in  a rotating  disc  sc  that  foe  puffs  of  air  impinged  periodi- 
cally on  the  .vator  surface.  Tne  waves  were  .:,aw.e  visiole  by  flasnes 
of  light  passing  up  throupn  the  tank  and  forming  a shadow  of  the 
waves  on  a frosted  glass.  Informat iorj.  t;ujis  pained  by  water 

waves  would  oa  useful  in  predictir.1^  one  similc^r  actio;^i  of  sound  waves 
in  ventilation  pipes. 

Tne  current  of  air  toroudi  tbf  re-^ist sr  box  scarcely  affects  the 
sound  waves  since  the  velocity  cl  t no  air  is  only  ab v. ut  0.09  meters 
per  seceno,  wnile  the  velocity  of  sound  under  nor-.al  ccnditioris  is 
about  bb?  meters  per  second.  Ooservatiens  taken  by  means  cf  this 


apcuratus  she  ed  ir  a.  jv-n:.r^l  •••ay  thit  tee  bCo*v:  ;-,7e£ 
t-ne  i*ei'i£t  :r  ocx  -as  -. n la  Fi  .e.  A t ' 3 C-.23 


v;ere  ^nterin;'  tQc;  racist  or  bex  tbreo-^n  t^:  voux  aoJ  “ 

r 0 C; i 1 1 > '.V ii  i c i-  X i:. t'-  0 o ^'L  ’’Vci s Ircaxod.  The  e.fXecx  of  a seri:- 


on  the  soanri  vvaves  >vae  then  tried  out  Iv.  ti.3  rirnle  vave  «iiachi..^e  as 
sh:.vn  in  Fi.  , <i.  A sov^xn;;:  t^eir  jenn:,;.!  effect  uiren  e.:terir._  the 
reoiet-r  box  fro;*  tne  roc-'n^  ani  B their  effect  u^ecn  souao  oao'es  eot- 
erirn  the  box  frc..  the  v-;:nt/  pijtas. 


7 


of  powar.  Various  devices  are  installed  in  these  imfflers  such  as 
concentric  charribers,  perforated  baffle  plates,  and  expansion  charr!- 
b ers. 

L.A.  Hardln0::  and  A.  C.  Willard  in  their  theory  of  ventilation 
likewise  bring  out  many  points  which  research  rren  could  use  when  in- 
vestigating problems  of  this  kind,  such  as  the  circulation  of  air  in 
a building;  the  effect  of  locations  of  inlets  and  outlets  on  air  dis- 
tribution in  rooms;  the  effect  of  high  velocities  in  pipes  and 
through  grille;  friction  in  various  size  pipes,  elbow's,  square  turns, 
and  enlargements  in  pipe  ares^s,^^ 

IV  EXPERIMENTAL  INVESTIGATION 

1.  General  Method.-  A standard  sound  generated  in  one  roor.;  pass- 
es through  tne  ventilation  pipes  to  other  rooms  where  observations 
are  taken.  Absorbing  devices  are  then  introduced  and  the  observa- 
tions repeated. 

a.  Source  of  Sound.-  In  an  investigation  of  this  kind  a 
source  of  sound  should  be  chosen  wnich  will  remain  constant.  It 
should  also  be  capable  of  variation  in  pitcn  in  order  to  furnish  a 
more  complete  test.  Voice,  piano,  and  other  sources  of  this  nature 
are  not  satisfactory  because  they  give  complex  sounds  that  are  not 
constant.  Tuning  forks  or  tone  variators  are  more  suitable  because 
they  may  be  kept  quite  constant,  and  different  pitches  may  be  used. 

A tone  variator  of  pitch  512  was  finally  selected  as  the  source  for 
this  investigation. 

b.  Receivers.-  A number  of  instrument-s  and  devices  are 
available  as  receivers. 

10.  Page,  V.W.  "The  Modern  Gasoline  Automobile^. 

11.  Harding,  L.A.  and  Willard,  A.C.  "Mecnanical  Equipment  of  Build- 
ings . " 


8 


1.  The  Ear.-  Supplementary  measurement 8 with  tne  ear 
are  quite  desirable  because  sound-proofing  is  usually  ins  called  in 
buildings  to  suit  the  hearing.  Such  observations  were  taken  in  the 
course  of  this  investigation. 

3.  Instruments-  For  more  accurate  work  it  is  necessary 
1 0 ob tai n quant i tat iv  e measur em ent  s wit  h ins z rum  ent  s . 

a.  Telephone  Receivers.-  An  arrangement  could  be 
used  as  sncwn  in  Fig. 5.  A Bell  telephone  receiver  a is  placed  near 
the  source  of  sound  in  room  A;  b is  a similar  receiver  placed  in 
front  of  the  duct  in  room  B.  By  means  of  rhe  double  pole  double  thrc  ^ 
switch  at  o_j  an  . observer  at  d may  listen  alternately  to  the  source 

of  sound  or  the  sound  transmitted  to  room  B through  the  ventilation 
pipe.,  A variable  resistance  _e  allows  the  intensity  of  the  two  sounds 
to  be  made  equal  according  to  the  estimate  of  the  ear. 

b.  Telephone  Transmitters.-  A more  sensitive  ar- 
rangement than  the  one  mentioned  is  shown  in  Fig.6,  In  which  carbon 
transmdtters  are  used  instead  of  receivers. 

c.  Resonators.-  In  order  to  reduce  the  complexity 
of  the  sounds  and  miake  tne  comiparlsons  of  the  two  sounds  more  accu- 
rate, resonators  were  attached  to  the  telephone  receivers  and  crans- 
miitters  to  amplify  the  definite  pitch  used. 

d.  Amplifying  Arrangement.-  Since  the  intensity 
of  the  transmitted  sound  becomes  very  weak  as  the  various  absorbing 
features  are  added,  a further  amplification  is  necessary.  This  is 
accomplished  by  means  of  the  audion  bulb  circuit  shown  in  Fig. 7. 

e.  Audibility  Meter.-  As  a check  on  the  obser- 
vations already  taken  or  to  determine  the  audibility  of  tbe  sounds 
from  the  two  sources,  an  audibility  meter  was  used  as  shown  in  Fig. 8. 


/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

; 

/ 

/ 

/ 

/ 

oA 


/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 


/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

W 


/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 


/. 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 


/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 


/ 

/ 

/ 


/ 

/ 

/ 

/ 

/ 

/ 

/ 


/ 

/ 


w 


Fi, 


Fi^.7 


F i ' . 6 


9 


This  consists  of  a constant  impedence  variable  shunt  so  arranged  that 
the  audibility  of  one  sound  may  be  compared  in  relative  terms  to  the 
audibility  of  a sound  from  a constant  source. 

f.  Devices  to  Stop  Sound.-  Sound  in  a ventilation 
duct  will  be  transmitted  to  considerable  distances  with  small  less 
unless  transformed  into  some  other  kind  of  energy.  It  is  not  suffi- 
cient to  reflect  or  scatter  sound  waves  for  the  energy  cannot  be  de- 
stroyed in  this  manner.  Usually  the  sound  is  transformed  by  means 
of  friction  into  heat  energy. 

Various  devices  may  be  used  to  bring  about  this  change  in  the 
form  of  energy,  but  several  factors  must  be  taken  into  consideration 
in  their  selection,  such  as  eddy  currents,  frictional  resistances, 
and  absorption.  Furthermore,  sound  insulators  must  be  designed  in 
such  a manner  that  dney  will  not  be  impractical  from  the  standpoint 
of  the  ventilating  engineer's  point  of  view. 

Sound  insulators  which  will  produce  these  results  to  a greater 
or  less  degre-id  are  concentric  chambers,  baffles,  hair  felt  linings 
or  combinations  of  devices  of  this  nature. 

V resuLpTS  of  investigations 

1.  Experiments  in  the  Smith  Mem.orial  Music  Building.-  The  venti- 
lation system  was  not  as  sound-proof  as  desired  and  appeared  to  be 
the  greatest  drawback  in  the  control  of  sound  in  spite  of  the  fact 
that  each  room  was  equipped  with  a separate  inlet  and  cutlet  duct, 
and  that  four  independent  ventilating  systems  were  installed  to 
furnish  air  to  four  groups  of  rooms  to  lessen  the  chance  for  the 
transfer  of  sound  from  one  group  to  the  others.  This  system  was  in- 
stalled as  Shewn  in  Fig.  9,  which  is  the  method  regarded  as  the  m.ost 
satisfactory  for  the  comiplete  diffusion  of  the  air  in  a room.-^’^ 

13.  Harding,  L.A.  and  Willard,  A.C.  "Mech.  Equipment  of  Buildings” 


m. 


r.V'  !'*■'’ j 


Z‘,A^n'i  i\\:  t’-'i  r//  ‘ 


I' 


[}^.:rA-.  •/,  " -.vV'i 


vfW 


I 


-jf,!' /it  ••;4s/.;.:  -«.•  ;*i ‘4j.>it:^ '^: b^' %4 1, j i V' . ii5« 

,i  - icl^  ^ 


ii,'J''ai^j4  ?I  . ' *J'T  •'■,%'  * ’ r'  ?.?  ^'.v  A; 


li*i^'-  ';j^s 


’ •2'“!?'  -'kVAj  "n- 


V • Qt  t'kl 


•« 

r 

m 


;4,'  .'iM 


«K,„ 


rt  ’ ■ -.  -.'■  ' V t»  - , ’ 


'^>.*i«rv 


!m  I » 

t 

W'  *■  ■ - ’"  • * ' T 


- /ft  : :.■;’ 

■ if”' 

! • ^ ” 

I x>;::'i 


* rM  ■ VPfe  - '.T«^ 


•fp 


"J<if  ' k <.  , 'ft  7ff 


nu«4l7  ■ . ■ > ; *,”  ‘f^’' 


> Ihv.'  i;;g?  , K^i 


8' 


- / ‘ i«C.Kr4^,;  p 


^*c:  ,:»“  /, 


V ...  ^ .%via . , _ 

. 4 V '♦  :■  :m  ' - r-<..(U  - 


‘ . 'M>'  ''V  ■ »|vvt‘ ' 

..■  ■■;  I < "I  1 f ' .i  -'  . . ' 

■■“»  Pj 


tin 


-!*«.-.  «4T  r-  ••.■■:: 


f < 


■'i'rr 


In 

t » 


/ • 


. ■.V 


r 


4.  ; ,;^t  y 


4V 


,MSNS  ,.,  “I®  W» 

m {^f  ■■ '1#?;  ' V 

jif' vTAuKuHn  '■  *»-'‘j#  ■*“'•-  ^^WPWI'r. 


• *1,  ■'  -.'.ft-i  ,-.'  ,•  j«  „.  - t'* '.  I ^ 


%1U- 


•^■'l/iiiaULm  'it/' W 


10 


a.  Outlet  Pipes.-  ITxper insnts  conducted  in  tne  build.inp 
after  its  coiMplet ion  ercugnt  cut  the  point  ticat  sound  was  transinitted 
t'nrougii  tlte  vent  pipes  to  tne  attic  space  ■^vhere  it  then  passed  down 
other  vent  pipes^  particularly;  those  adjacent:  to  the  one  emitting:  the 
sound.  For  instance,  a sound  generated  in  Professor  Van  den  Bern's 
studio  (Rocn:  113)  on  the  first  floor,  south  corridor,  passed  thrcugh 
a vent  pipe  to  tne  attic  and  then  down  other  vent  pipes  sc  as  to  he 
easily  neard  in  Professor  Johnson's  studio  (Rco.;.  215)  on  the  second 
floor,  and  a practice  studio  (Roon:  303)  on  the  third  floor,  as  ;vell 
as  in  the  t.'o-N  sr.'s  Chorus  Roon.  in  the  ‘oase.rent,  directly  under  Rocrr; 
113.  These  vent  pipes  were  arranged  as  shown  in  Fip:.10.  Fir.  11 


'i-.  11. 


T#*  , ^ 'Fl;  ^ "W*;  ::; 


|i  1 ^ ij 

I i,  ■ ■•  fl 


f>  I 


i ' '■ 


Cv^I 


■*^''*»\  -»  »-  «*W  i«*  -•  «—  i(-«^  »iw(^*» 

■%.  ^ WT- 


V I 


r; 


rM 


r :« 


fff:  irtiBf 


•h.* 

"’iit 


0 


P Vi:  i'  *'-ii^4  i'>u  4-..,  '*  ’-‘  't;*- 

. feJhtl^<NI»^i^i  ■’  fA  ' \,I-.  II’  '<,i^n>'M’  ,i..ijVX*t|'*'  ■■•  [Imfe'i 

t-  ' '^  d.  ^ i * I ^ li^  uift)>npxBHABti^nlW^/V^( ' 


'.'  I 


!.Q  ■'*  2>  I - w -t  ' ■'  >Hl 

■ ,'•'  ' . r-  - M 


r' • , ’ 


“1? 


I # » ' <► 


»v 


'3l  \ i*  .j.  r#.*f:>i^i  . 4- , Qi  x|-.  r at'l 


^ ’ * «iff 


I. 


i.  ,*<"  • 


•4.*  “'• 


ti 


■■'■.*  Wit  ; ' ' « .*.5  A 


Ji  ''it‘  ^ , 

' {'/  \ \ n'>-r„ 


>'"■ 

'■  : 4 t™ 


A11 


-'.j 


SKI 


t ■ * » 

m I , ■'■ 


Jh 


■!  'U 


i 


If  »^»»»  *>-«*  5'h"'!>’f ‘'Up  ' ’ 

" ■ .P.  ■ t „ ' : I ; ,;L.,„ 

..  . ■,.  ''  f 


> ,a 

W .'f 


' ;'  ' ^ ' 1)  , 

m .'  - 


W- 


. ^'■ ' ' f-  ■ .•;V,  Ju  .- 


,-r^,  |■'“f 

# fr.r^  . 

I ! :!  K.«"kvV:?if!, 


J: 


k"/  / >• 


A'  ■ I. 


?,r..f£u* 


-Vi/'  , 


u2  <' 


' M: 


HALL 


/U/Vi 


PLA/v 


Outltt  Pldri  fv-r  S.^’.  Ccrn  r Psction 
FiP-,  10 


Fig. 13 


Fig. 13 

Phot OgrapJTiS  shewing  the  entrance  of  vent  pices  fro.-  Rooms 
106,  308,  o30  an;"!  fro^  the  haserr.snt  into  the  attic  space. 


22 


stLorns  another  typical  case  where  these  vsnt  pipes  enter  Xh>^.  attic  -^.'d 
illustrat '.ts  the  possibility  for  sound  transmitted  throu;,-]'!  tMe.-r,  to 
pass  down  adjustnent  pipes  to  other  rocais.  Fips.  13  and  Ic  are 
photographs  showing;  the  entrance  of  this  particular  set  of  vdpes  into 
the  attic.  In  this  case  a sound  genarat-^d  in  a practice  room  (rjo. 
330)  on  the  third  floor,  north  corridor,  passed  tarougn  a vent  pipe 
to  the  attic  and  then  down  other  vents  so  as  to  be  easily  beard  in 
RoC::  208  on  the  second  floor,  Rcoii  106  on  the  first  floor,  and  in  tee 
basement  room. 

To  reduce  the  transmission  of  sound  through  these  pines  caps  were 
designed  to  fit  over  each  of  them  in  the  attic  apace  as  shown  in  Fig. 
14.  The  attic  portion  of  a typical  vent  pipe  is  shewn  at  a,  b is  the 


Fig. 14 

cap  designed  to  m,inimiizs  the  possibility  ot  the  transfer  of  sounds 
between  tnis  pips  and  adjacent  pipes,  c_  is  tne  galvanized  iron  body 
of  the  cap,  d the  hairfelt  lining,  and  _e  supports  to  held  the  cap  on 
and  over  the  pipe.  The  lotted  lines  in  Fig.  11  show  the  outline  of 
a set  of  tucse  caps  f^r  this  particular  set  of  pipes.  Fig. 15  is  a 


1/ 


J 


,.-  'I  * . •!  ' ^»  "i'H^  ,_ 'iliJ 


CT*4  ^ ' ‘■‘■  O ' t / V c*''  i:.jt' 


Ku.^!,.  c Tifftn  /fK(L  ;rl 

: " ‘'■J  , - . .|  ' T;^r 

":*  ?i-  ;’  >'i/*4’  Iqi  V , tJ* * j.xtf  ^-iroL 


# ■^‘-4 

.4.; 


^ f: : ' f 


i<- 


■ r,,,,:^yi 

»,■  . _f,  ■»  . ■ •■  , ■ *.  / «• 


I 


k:  r /■ 
? ■ 


i . 


■''■''‘‘'f*!'=  ■'??  - 

' -^  -Mi 


4 


*^ , ..j^. 


^1  /kTi 


<b 


. * « 


13 


Fig'.  15 


Fig. 16 


14 


photograph  shewing  the  caps  resting  on  the  particular  pipes  for  which 
they  were  designed,  and  Fig. IS  shows  them  installed. 

Observations  made  with  these  caps  in  place  and  removed  from  the 
pipes,  verified  the  assumptions  mads.  For  example,  when  a sound  was 
generated  in  Room  113  the  intensity  of  the  sound  entering  Room.  315 
and  Room  303  was  practically  negligible  sc  long  as  caps  were  placed 
over  the  pipes  from  Room  113  or  when  the  cap  was  placed  over  the  pipe 
from  Room  113  and  the  caps  for  the  pipes  from.  Rooms  215  and  303  re- 
moved. When  the  caps  were  placed  over  the  entire  set  of  pipes  a 
sound  generated  in  any  one  of  these  rooms  was  greatly  dimiinished  In 
its  transmiSBicn  to  otner  room.s.  It  should  be  stated  that  these 
caps  scarcely  affect  the  ventilation. 

Consideration  was  now  given  to  a m.eans  of  minimizing  still  furth- 
er the  intensity  of  sounds  passing  through  these  vent  ducts.  Hair- 
felt  was  placed  on  the  walls  and  bettemi  of  the  pipes  where  they  ent- 
ered room^s.  Observations  shewed  very  clearly  that  the  hairfelt  lin- 
ing cut  down  the  intensity  of  the  transmiltted  sounds. 

Another  device  consisted  of  a series  of  baffles,  made  of  wood, 
padded  with  hairfelt.  A marked  decrease  in  the  intensity  of  the 
transmitted  sounds  resulted  when  these  baffles  were  installed  In  the 
outlet  register  boxes  as  shown  in  J<‘ig.4.  For  exam.ple,  with  the 
source  of  sound  in  Rocmi  113,  a decrease  was  noted  in  the  intensity 
of  tne  sounds  transm.it ted  to  Rooms  215  and  303  when  baffles  were  in- 
stalled in  the  register  box  in  Room.  113.  A further  decrease  in  the 
intensity  noted  when  baffles  were  also  Installed  in  the  register 
boxes  in  rooms  215  and  303. 

Additional  observations  were  .made  with  the  three  Insulating  de- 
vices previously  described,  namely  the  caps  on  the  vent  pipes  in  the 


! 


: i 111)  Ki  i-tii»^;.ir 


'r-jT  . .-  . 


r • 


J- 


' ‘ ' I •'  '^hU^Hk 

■V^ . "f,'"  1^’'?  V ' ■■  ■ ' ' 

- - i w ^ ^ A ,v;. . . j: , . 


V 


•^c  .4;;;  e.C‘5. 


fif 


/■'".‘’‘‘’I  , — :>■; 


I ■•5.  « ' ‘ . ‘ ■ 


t.'eS  I'*'  V'- -"i-jr 

* 'i^wsl  Aft  il  'til 


r.ar«tfry4?t' 


'T'^i  ' f'# 


M 


>T'  v;  .™ 

. ...  ' Ji^:: 


••♦  4 t ■ # V'  •>'  .iV'ttVa  • j'H’ 


• * ‘M  .>  '#N.  'Fi^ 


i ;;  V>  ..r ..  4 ’ AVi’  '■■■•C#  ' '*  * ■ * 

» * ■ , .-  ■-  '■■-  j *6  ,5^.,  .‘'  y 

* ;i,  ,5‘)  Jlc-^L  / ;a 

’.  ;*  .A  j . ‘ •!  , "V ' 


!S 


1 • 


• j : <*  r ' ?.  f-y  . villi'  j’  ■'' 


'^•9  th  fl'i  V .'.'  J 


Jf 


V.  n.  ♦ mi«.  . ..w 

-■ 


M#l"  ' 


'■  .4  'J':  ■ 

...ajC'j  I'-iiiUi;*'  » v^'  T'  - '-ir'  ', :<j'4' ♦» 

. ; . ■ :*'  ■»*  / • 

V '.V,'.,  :-3<*.  ^ T6 


‘-  -'^  • 


t^-  -'!»;t ''“ '•r,”  f .' ^ 


ftl  *y^t  t ‘ '*4 

f*.  " '-,ii.  :1*L  ' >:,f/‘ 

t'.'t  'X  . . ■ ■ t y- 

. ; /'v'H 


ft  f*  ~ 

\ “ 


. ••■/  . 'WAy^“W‘  , /*:  ;f  .•  vA  ' 

->.4  tij^j  • . . .;  »r>ii 


J*/  ' i' 


I.  . I.  .fA  I, 


15 


attic  space,  the  hairfelt  lining  in  the  register  boxes, and  the  baffle?: 
in  the  register  boxes;  arranged  in  various  cc/rbinations.  When  these 
devices  were  used  together  little  or  no  transmitted  sound  could  be 
detected,  showing  that  the3'-  afford  a satisfactory  means  tor  the  con- 
trol Of  the  sound  in  ventilation  pipes. 

Little  or  no  effect  was  noted  in  the  intensity  of  the  transmitted 
sounds  when  stops  made  of  galvanized  iron  padded  with  hair  felt  as 
shown  in  Figs.  17,  IS,  19  and  30,  were  placed  in  front  of  the  cutlet 
chambers. 

b.  Inlet  Pipes.-  Inlet  pipes  permitted  sounds  to  be  trans- 
mitted from  one  room  to  another  as  well  as  the  outlet  pipes.  The 
i.nvestigat ion  was  now  directed  to  these  inlet  pipes. 

Four  independent  fan  systems  are  used  in  the  building  to  furnish 
air  to  four  groups  of  rooms,  sc  that  the  transfer  of  sounds  from  one 
group  to  the  others  is  lessened.  One  system  supplies  all  of  the 
studies,  one  supplies  the  recital  hall,  and  two  others,  situated  on 
the  third  floor,  supply  the  practice  rooms. 

The  inlets  are  all  placed  above  the  breathing  line  as  shown  in 
Fig. 9,  which  is  the  proper  location,  according  to  the  best  authori- 
ties on  ventilation  to  give  a complete  diffusion  of  the  air  in  a 
reem.  The  inlets  for  the  rocn;s  already  discussed  (Nos.  113,  215  and  ■ 
303)  and  which  serve  f cr  this  invest igation  since  they  present  typi- 
cal cases,  are  arranged  as  shown  in  Fig. 31.  The  inlets  for  Rooms 
113  and  215  pass  down  through  the  corridor  wall  to  the  basement  where 
they  are  connected  tc  the  system  supplying  air  to  the  studios.  The 
inlets  for  the  practice  rooms  (Nos. 303,  307,  etc.!  pass  up  through 
the  corridor  wall  to  the  attic  where  they  are  connected  to  the  sys- 
tem supplying  air  tc  tne  practice  rooms  on  the  south  side  of  the 


i 


w^nrr. 

I.-*  ' * 

i>' 


! 


-,..V., 

■' iMi<|ft^Vair)r^.4i,<i-i7i-eTi>?:»>M-T<^ 

' V'^  ’*  ' - "“ 


• V ■■  ; ’'  Wt^ 


,>,  ■ . - ' / 


^ ^ -aiif 


5" 

4*; 


X 


. r'7.’  ..  *v*?t|  tii^jyi^LLi'ti^v:  ni  ^ 


-•  f ^ /'^'i  ‘liMJji^vj;i^  to  «;- 


|tl^» 

IV 't' 


i.‘i? 


'tOJ;  l^jfr^€Z- 

*■%***' TS-.  ^ t vj'' 

j ...  ^ ■ J w9 .'  I j ..  1 


% 


T 1‘ 


' ■*.  . » 


m • .rli%.,?f.<ji-{5.v.‘i 


Ht- 


1- ^■..‘J'^I  .M(k  2 \A  •'•'*,**  *■ 

:■  •.-  ■ - 


'i-v . ; it*i4  1’^l- f 4> »!.yjf<5ft >V»f 

• . JL^  , " "■  •> •> ij •■  ■ ■■  i5 *;• . . -4;  e.X r V .^  '•  ‘ 

-.I’l*  -V-  ---i  ■*  .L-  ..n^,  tf  t'-f'fri.y- fv  f T^"’ W' 


♦ • • 


'.  •n’l  X.  ,*«J 


X i fr?’! 


i - . C^t . . ; toi«ikt»«l^  • ■ u •'  ii*4. ' l^.'  4'd  ;U't'  i 


L i 


ib4|l 

' ' L i.i  ■ :' . ; a*.  .•;  < >•. • - ‘ ‘i:'  I',  •fij'-j : : jS^i . , ■<■  w jRT, * 


i V 


;.  '.  .V."  '■  €y-  «pp^l 

."  *.,ii'  .if*  jjMtKfl*.  \W'#  ■fi5?f','"iw 


Iw  .^*<1  ’ ' ‘ 4Z'<vQ*^i(vV'V  '.*CT>  ’’  '*' ' >n 


Fij.SO 


..»fc«U--*->P  fti  ‘iriiKfi  ikt<t ‘^>i^li\jl^»  t 

*•  T-.*.  i 

.V^‘  d 


'f  L 


’^ui-  <k-Wtijr. 

’ ' ■./<* 


■ ’ -W. ''  "I  . 


*v 


I'U 

k f . «.%  '« 

•A  ; ^ 
f,.,4l'  i' 


,y*  - 


I J%.  r^ 


■ii’l  J^,  > t^,t 


17 


Inlet  Plan  f-r  SJ''.  Ccrn.ir  Section 
Fi,;.<el 


4 ■ _ 


teiiliim  >Ji  I gifu’i'  ' 


T*-'  P 


'>■ . .'T 


'T* 

W'^ 

j 


E 


k * >1i 


;'^yq 


' ■■'V  V 


•/<,-■ '’r- 


. ...  ■.^,a  ■'<«■*/? 


‘/■r'  ^ 


S’  '■^'<1  >'i^| ',»a 


;:j  _ »,  *,11  [i / .>1 

4 f..  P '-.Ly 


ii  i' 


tf-'.r/! 


i: 


y -j  ■-i:rmm 


I 


t'.  I 


i>  ■•-«  • 1!  •>/  4UW  'fu— ■•#•.*•  I 


V 4M"  ■■ 


[: 


Vn 


, , . Rf,j»  at  ^ 


;,.\V|*  >1^  Cfl 

til  *-Wv  ^ > .'■■./i'J^J^'’-  *■  '■  ■' 


V,; 


fc  »'jfc  * , — 

,'v.  . ..■  .-"T 


i^-y 


1*  ^ • 


iWW  **'■"•  ■ •*•  •:  p-- iiwi» j|«i v 


IS 


buildin^ . 

Unf  crtunately,  ca^  3 oai-.nou  bs  placed  c-v  ■ r t i*oSb  :=s  aS  :lu  t;,  :. 
case  cf  ti'-o  outlet  pi]: as,  therefore  bii3  inf cr.*.a tier..  ootai..ect  ix^  t o-,-? 
i'. cevious  inv.stigatim  is  net  directly  at  lico. '■le  in-s  r-fa.r  as  the 
inlet  riyes  -.re  ccncerned. 

The  register  boxes  connect ing  the  inlet  piyes  tc  the  rco.-s  are 

id  in  tx-;e  case  of  ;tne  vent  ducts  exc-3T''t  for  the 
are  ir-.st ailed  as  shc’o 
;d  in  the 

the  cos srvat ions  repeated.  The  cesults  a,rreod 


similar  tc  these  us 

fact  that 

’Splitters' 

similar  t 

c those  us 

tne  ixiiet 

00X33  ana 

with  the 

obser  . -tic. 

13  uutlet  re^^ist'r  bexes  »vere  installed  in 


a rcu,- h uha 


o i' 


'.vas  practically  ne^lioible.  ^'■ithcjt  those  insulatioo.  devices  it  '.ve 
observed  th^t  tne  t r-nsuiit ted  ccund  ':-s  ^r-:;.at -.■r  in  rcc:..3  directl3’’ 
adjacent  tc  tb.c  sound;  tn^t  is,  rco.es  directly  ever,  under,  and  by 

the  side  cf  the  rooi.  ccnt-ini.vt  th^  scu.nd  source,  but  this  is  zc  03 

expected  if  the  friction  at  the  elbc;';s,  etc.  , in  toe  systen.s  are 


.*  ^ ^ ' . ■ T 


r? 


' J'  * I i:  : “ “ ■ I ''  t.  -:’  'Jt : 1 1 J 

Ss  -’■-’ 


0J( 


'■  '/■'  ^'.Vt  t ’*^J'  . * \ 

^ ^ \ i ' ' '^'1^'*  ; 

' ' '.'  uA  \ ■ * ‘ ''MU 

'■i  ’•5^.. 

. . . . * . ..  

t-  ,.-^-ro.-j 


M .> 


h/>  , I 


ic.  .-3 


t;J 


f *j. 


ri 


r ' i \ i'  *i  <*4^;^ 


' a , r 

* I ' .« 


f;  .'ifi  *Tl^  ‘ <7*. 

^ '.  i 


-4  ,-• 

.'.'■V"'-  ■ 


4!. 


.'  4 


m ^ * ^ W V'l  “> 


■ Ii  ?;.>>-.• 


' *—  -- ' 


\..  '••  ■ : iK>i„.- 
\ ,'f~'rr  ' ' ' 


I r 


i‘  I 


V'  * < .yJ 


I #. 


■ 4 w.f.i 
' hf 


- i'  fji 

r'  t.-'^Vl 

'‘1,  u ' . ' ** 

,.  ?l! 


■ 1 


.'■0.  J 


'5>;yC,j.' 


fd  i } ■ ' ' ■:  .\  '.m  . "■  :Wv.-  ■'  ■/  s ■•.-W'ffi  . ^ 

sfl^MSj  ,v».  -. :.  imm' ,»;» 'i. -..•  i.’.tua^  .■**(«.  mmUm 

fiC  ".'  . ■ ".  .i!lM 


r 

l-'Vi, ' 

.V 

b';T  t 

» *i 

*' 

>1  f''.  ' , 

Jim.  IF' 


I !>'.  ■■*;^  < 


f)  ,^  ' ' '-1  ,.  ■ ■ ' ^. W] 


* '.•  W.  <’  .7  < ^,'  V ,'  '’,'.^M>f<f,  V.VJ-W  .L^  ' a 


.V  ^.  ‘ V iv  'V/i' ' Clirtl.  *4^ 


19 


taken  intc  consideration.  Snow  in  his  bulletin  "Voice  Pipes"  also 
brings  cut  this  point. 

Ventilator  stops  were  placed  in  front  of  the  inlet  registers  sc 
as  to  cause  a spreading  effect  of  the  air  current.  These  stops  did 
not  have  an  appreciable  effect  on  the  sound  and  are  inipract ical  fron: 
the  standpoint  of  the  ventilating  engineer  and  were  therefore  dis- 
carded. 

A further  test  was  made  regarding  the  intensity  of  the  sound 
transmitted  through  these  inlet  pipes,  with  all  insulating  devices 
out  of  the  system,  namely,  the  air  current  was  turned  on  and  off  and 
observations  .made  but  no  difference  was  noted.  This  was  to  be  ex- 
pected since  the  velocity  of  the  air  was  only  0.03  meters  per  second 
and  the  velocity  of  sound  in  air  is  3b7  meters  per  second.  A higher 
velocity  of  the  air  would  no  doubt  have  generated  a new  sound,  name- 
ly, a humi  of  the  grill,  which  would  not  have  been  affected  by  the  de- 
vices installed. 

3.  Experiri.ents  in  the  Physics  Building'.-  Further  experiments  in 
connection  with  this  investigation  were  carried  on  in  the  Physics 
Building  at  the  University  of  Illinois,  which  was  conveniently 
equipped  with  research  facilities.  Many  of  the  troubles  experienced 
in  the  ventilation  systems  in  the  Smith  Memorial  Music  Building  as 
well  as  in  other  buildings,  where  such  systems  are  used,  are  like- 
wise experienced  in  this  building.  The  work  could  thus  be  carried 
on  effectively  and  without  interrupt  ion,  which  was  not  true  in  the 
case  of  the  Music  Building. 

A typical  case  selected  for  investigation  was  the  ventilation 
duct  between  Room  317  on  the  third  fleer,  and  aoom  217  on  the  second 
floor.  The  general  method  of  attack  previously  described  was  used. 


i ^*1  t^'in\  .iia^gM 


‘li 


I r ;.-;.-v  ;/i«'fl.-ji*J^i  . ' P .U:,m 

‘vijl  a*' '•fr  il'i  -y  i'*  eit!  r|)'l.4'’  ;J,-i^ 

( ■ » '4  J'l/ 


f'  :•'*! 


,^^'*v  t t ' ; ;:-.  ^ i\  A -'J  • i 

i;  i: 


t<  i\ 


4*  - 


e.t- 


■:•'  A' 

*••  r • V 


^ j r.  i . i t)'i . -s  -i  » * :..,  •.  i-  r.  /■,  tff/  :' 


ki 


I *>■  ^ • 4 t * ' A'  .'  r 
I 


.,  •-»  ' .’.T.i."  ■ I 

11  d.'i,  5.t-- i ^ 

’■'^ -^  A.  , . '•,.  > ■ I 

,.*i  /Ua  ‘•^^^l,i■|^'o^:f,  I 

' ■ ^ ; ■';  ^ y-j  y 

iVt  CM  'i  .■^  f 4V''*LA'.yi 


■ )i  '.  1 


I «. 


ti  * 


»v  u 


y.  C,.  '1  .'  .'iT.r  e.f:  |£-A  ; i,  iJtr-Afitf 

' * ^ ' ^'‘J:ilM  « ■■J ■ '',  r~^  '-'»  ■-■  C..sijgi^  • J 


J ■:.r- ■ , ,'.  '.^VV'V 

. ■?  ''M?® '■"  : 

^ ' ' ySi  • .*■:.••  • 1: . :>..J life  •■  ■•  .1  4 dMBL>>  i’iiMsiPS  l 


30 


a tone  variator  being  installed  as  the  constant  source  cf  sound  and 
the  oar  and  the  various  other  devices  described  above  as  the  receiv- 
ers. The  tone  variator  v;as  placed  in  front  of  the  grill  in  Rccir  217. 
A Bell  telephone  receiver,  to  which  a Helrrjholtz  resonator  was  at- 
tached, was  placed  near  the  variator  and  ccnnected  to  the  double  pda 
double  throw  switch  in  Room  211  as  shov-m  in  Fig.  32,  A sensitive  tel- 
ephone transniitter  to  -which  was  connected  a Helm'holtz  resonator  set 
for  the  particular  pitch  emitted  by  the  tone  variator  was  then  placed 
in  front  cf  the  grill  in  Room  217,  and  also  connected  to  the  switch 
in  Room  211.  An  induction  coil,  a tv/c  stage  amplifier,  an  audibility 
meter  and  finally  a w'ireless  head  set  were  likewise  connected  to  this 
switch  as  shown  in  the  diagram.  When  the  audibility  meter  was  thrown 
out  of  the  circuit  and  the  double  pole  double  throw  switch  moved  back 
and  forth,  the  intensity  of  the  sound  from  the  two  sources.  Room  317 
and  Room  217,  could  be  balanced  against  each  other  by  means  of  a vari 
able  resistance  placed  in  the  circuit  leading  from.  Room.  217.  The 
variable  resistance  was  placed  in  the  circuit  from  217  as  the  intens- 
ity from  this  constant  source  remained  the  same  at  all  times  while 
the  intensity  of  the  sound  fromi  Room  217  varied  according  to  the  in- 
sulating devices  installed  in  the  pipe.  As  a further  test  on  this 
system  an  audibility  meter  was  thrown  in  the  circuit  and  readings 
taken  cf  the  audibility  of  the  sound  from  the  two  sources  after 
they  had  been  balanced  against  each  other  by  the  first  method.  The 
results  checked  shewing  that  the  ear  is  very  sensitive  for  compari- 
sons m.ade  in  this  manner.  A difference  cf  a tenth  of  an  ohmi  in  the 
Variable  resistance  could  be  detected  very  easil^r  in  the  first  m.ethod 
of  balancing  the  intensity  cf  the  sound  fron.  one  source  against  the 
intensity  of  the  sound  fromi  the  second  source.  Data  w-as  taken  for 


Lt  T ;,  U'\t  if  (*Sf  * W 


%4'-M  1C 


■ *'  - .^  .,»  ,1*^.4- . - tir.  Xii'.  31^,11 


3-' 


. 

. ;*  i .H,'  1. 


F' 


♦ * *■  *-•  I i-  * * ■ ■ V ■ (H  i Hf^tVl  \ 

t t '»/  ‘ ?v'.fia  |i|p 


.1^ 


).)^il  ;.:  -'I;--..  I» 

» % 

V **-r  ro'C,  f.'f(<>vH*' 


•i®ii  /i  'i-« ^;»iiijij^<t -iMrAiawi  - 

■;  v.,  f^-' r •'(.  r Tf.i  fviciir^' ^ ■’‘t’Xp  ' ^;:ilii!^^'  i)  ' 

, '-■-  *■  , , •‘V'^';>/-  ■ ^':'f  ■ 

v*.v-  .►  *^  tT''*  ’ vii  .t  ^ 't  - ■•^.  - l1  • i:*  ■ . ^ ! i ^ i 

;^-J  ■“  'fc:  ' v;  ^ 

\ ^ ■ t!.  ■ 'it  j^i'OIipS® .^  'tif ,. 

^ r.J*'  ' ' ■',  ',;:M:y  ^ ,•  • TS 

’‘-i  Xf  ■ 

■ »■  * • A>  • ‘ irila — Yf  if 

■ ' ^ V'  > . ■ :„  ,*j  'i  4. 


h:  . : 

■"  i;^■ 


K jC  ,‘‘  V^ 

;?/  ^ , t^iX  w • A , : V t^{  . 1 1 ^ ■ 


4-  ■4*X^;^/1^i^ 

MAL 


j .«&'■':  ;'f5’ 

fl . '. •''  • ' ■''  ’4'?^"'  ■•■•  .^‘jl  ■ ‘*’') K’i‘^ 


'■irr.Sf 


^Vl*: -‘i,  ■ -*'v;  ■ . , . 


Arrarir  3--ent  of  used  duri*; 

in  the  Physics  Buildir; 
P i i 3 


tnc  experi.i. 


these  observations  as  shown  in  Table  I. 


CJO 


TABLE  I 

Observations  Mads  in  the  Physics  Building 


Test 

Room 

Audi- 

Ohms 

No. 

No. 

bility 

Res. 

Remarks 

1 

317 

74 

0 

317 

74 

1.6 

Flue 

free 

217 

46 

0 

317 

43 

1.0 

4 baffles  in  flue  in  Room  217. 

5 

317 

36 

0 

Same 

as  test  No. 3 with  a similar  set 

317 

36 

0.8 

of  baffles  in  flue  in  Room  317. 

4 

21? 

29 

0 

Sai/i  e 

as  test  No. 3 with  4 baffles  just 

317 

29 

0.  S 

back 

of  grill  in  Room  317. 

5 

317 

32 

0 

Same 

as  test  no. 4 with  4 baffles  just 

317 

22 

0.5 

back 

cf  grill  in  Room  317. 

6 

217 

18 

0 

Same 

as  test  No. 5 with  4 more  baffles 

317 

18 

0.4 

just 

back  of  grill  in  Room  217. 

7 

31? 

14 

0 

Same 

as  test  No. 6 with  4 more  baffles 

517 

14 

0.  31 

just 

back  of  grill  in  Room  317. 

The  data  given  in  Table  I are  given  in  a curve  (Fig. 24)  in  which 
the  resistances  which  were  introduced  into  the  Pl7  circuit  to  diniinist 
the  intensity  of  the  sound  froa  the  source  in  Room  bl7  to  the  intensi- 
ty of  the  sound  transmitted  to  Room  217  were  plotted  as  the  abscissae 
ana  the  audibilities  of  the  transmitted  sound  as  the  ordinates.  This 
curve  snows  the  decrease  in  the  intensity  cf  the  transmitted  sound  as 
the  various  insulating  devices  were  installed^  and  also  gives  the  di- 
rect relation  between  the  audibility  cf  the  transmitted  sound  and  the 
resistance  necessary  to  reduce  the  intensity  of  the  source  sound  to 
that  of  the  transmitted  sound. 


io 


Audibility 

in 

relative 

amounts 


Rssistanoo  in  OuihS 


Fip;.  24 


VII,  DISCUSSION  OF  RESULTS  AND  RFC OUMFN DAT IONS 

Tne  investigation  brings  out  tne  follov/,ing  points:  That  sound 

is  transmitted  from  room  to  room  through  continuous  piping;  that 
tnere  is  less  loss  of  intensity'’  in  large  pipes  than  there  is  in  small' 
er  ones;  that  pipes  themselves  are  set  in  vibration  if  their  walls  ar 
thin  compared  witn  their  cross-sect  ion;  rhat  outlet  pipes  opening  in- 
to an  attic  space  allow  the  transmission  of  sound  froin  room  to  room; 
that  linings  in  pipes  cause  a part  of  the  sound  energy  to  be  trans- 
fcrm.ed  by  means  of  friction  into  neat  energy;  that  tne  air  current 
has  practically  no  effect  upon  the  sound  waves;  thar  me  intensity  of 
the  transmitted  sound  is  greater  in  rooms  directly  adjacent  to  the 
sound,  tnat  is,  roon.s  directly  over,  under,  and  by  tne  sice  of  tne 
room,  containing  the  sound  source;  and  that  transmitted  sound  may  be 
controlled. 

In  accordance  with  these  points  crougnt  out,  the  autnor  recon- 
mends  that  separate  systems  should  be  used  for  various  sets  of  roorts 
in  order  to  lessen  the  chance  for  the  transfer  of  sound  from  one 
group  to  the  others;  that  pipes  should  be  made  or  ncn-vi’orant  h.ateri- 
al  so  as  to  avoid  nev;  sounds  being  created  within  tne  pipes  tneimsslve 
as  well  as  to  prevent  the  communication  of  these  sounds  to  other 


■ 


aL-J'2uata^ 


. 

r * ^ T ' 

, ^ - ‘ ■■  C 

’i^>."'*’  **'i;*¥?**-^*^”-^ 

- n , •>.  ? '*'  ' ^ ■-.vV' 

’*;■■■'•  i -C^  « *.^ 


V 


■.»  * 
♦ > 


P A 'i 

4 v Ifc:-:^  * 
■i^  *»V4 


2 


*»•»  • 


fi  ' 

VS>*.  •,'VV-  '4t 


7''^  ^ ■ ... 

•#.•«  .vvWT»t*s-  ■-•^ 


-^,  — i«W’<jt'  f' 


t-fda#.  in  ‘ „-j  ii  r^  A •,  ■ •"''"' ,' , 


f ' 


i ' W 

,‘W' 


■am!  •'..V/ 


I 


. I 


i 


I 


i,.  ' ’- 


t ^ 


■ ' f <■',; . . = k-  HC  '3)1 '( ii'ir.U  . t t-fiMlfm.. 


■'?V, 


' li* 


. i.i 


■ ')‘ii  t 

.,  . ••'"^  . '■  ■"■ 

4 *.  : .».^^  .'u  t^tX;rJ{£t:  ' A 4U-W’i 

X ^ « './.lii'lib 


■■.:i  ■■  ■•  i'.  .'*•  { >:,nU. 
in;  J 'uVi-n 

'*’  ' * ' J ' >1  X'J  Tj  1-  ''Ja  "'■  •■  I ■ I 


y.i' 


; f :'?. 4 U*  ^ y t r-  '. ^ 6-  4ft 

' "v.i  ■ - , t t ' ,V? . 

1 .,j  '!fl  XwJ '',  «;■  ) i,  , : k^.lili 

'•<  .*■:,;  ' .'tS’j.  ' ■ ■'>!:; 


n 


34 


pipes  "by  ir^eans  of  syiijpathetic  vibrations;  that  caps  similar  to  those 
previously  deecrlbad  be  placed  on  pipes  which  open  into  an  attic 
space;  that  pipes  be  lined  with  some  sounct  deadening  macerial;  that  a 
series  of  baffles  be  installed  in  the  chambers  connecting  the  room  to 
the  pipes  or  in  the  case  of  thin  walls  where  cnambers  are  not  used, 
in  the  pipes  themselves;  that  inlets  be  placed  in  the  room  above  the 
creaxhiiig  line;  that  outlets  be  placed  in  the  room  near  the  fleer  and 
on  the  same  side  of  the  room  as  the  inlets  and  that  pipes  from  dif- 
ferent rooms  be  placed  as  far  apart  as  possible. 

The  author  desires  to  express  his  appreciation  to  Dr.  F.R.  '’^atsor 
who  suggested  tnis  probleiK,  for  his  continued  interest  and  sugges- 
tions during  this  investigation. 


4 


